Harmonic generating and selecting system



Patented Nov. 1, 1932 UNITED STATES PATENT OFFICE CLYDE R. KEITH, OFALD'WYGH, LONDON, ENGLAND, ASSIGNOR OF NEW YORK, N. Y., A CORPORATION OFNEW LABORATORIES, INCORPORATED, YORK Application filed June 19,

This invention relates to a system for generating harmonics of any givenbase frequency and in particular to a simplified arrangement for uses inwhich an economy of apparatus and a minimum of attention for maintenancethereof are important considerations.

It is well known that by application of the principle of multiplexing,for example, by means of a system employing a plurality of carrierfrequencies, a single telephone line may be fitted to provide severalcommunication channels carrying a plurality of messages simultaneously.It is evident that multiplex operation saves the cost of installing andmaintaining a number of additional telephone lines sufficient to carrythe same num-' er of messages. It necessitates, however, an increasedexpenditure for terminal apparatus, the cost of installing andmaintaining which must be kept below the cost of providing theadditional telephone lines to eflect a net economy.

It is in some cases advantageous to provide merely a minimum number ofmultiplex car-' rier channels per line, for example, by the installationof what is termed a single channel carrier system, which provides butone additional channel per line. In this way it is possible to utilizedapparatus of extremely simple design, thereby reducing the cost andeffecting a substantial economy.

The system of the invention is particularly useful in connection with acarrier system of one or two channels in which it may be use to supply asmall number of harmonically related carrier frequencies with a minimumof apparatus. In a simple form of the invention the second and thirdharmonics of a common base are developed and used respectively as thecarriers for transmitting and receiving a single carrier channel.

An object of the invention is to provide a simplified system of harmonicgeneration.

Another object of the invention is to provide means for separating thesecond, fourth, and other even harmonics from the first, third and otherodd harmonics.

A feature of the invention is the use of rectifying or modulatingdevices havingno nected into this bridged circuit TO BELL TELEPHONEHARMONIC GENERATING AND SELECTING SYSTEM 1930. Serial No. 462,169.

more than two electrodes each as, for example, the copper oxiderectifier disclosed in U. S. Patent 1,640,335, issued August 23, 1927,to L. O. Grondahl.

In the present invention, a current of the base frequency is supplied totwo rectifying or modulating devices having two terminals each,associated with a three-winding transformer. Two substantiallyindependent systems of load circuits are provided in a balancedarrangement whereby the odd harmonic frequencies may be accentuated andutilized in one portion and the even harmonic frequencies in the other.Simple tuned circuits or other selective devices may be provided in eachportion of the load circuit for selecting the individual harmonicfrequencies.

In the drawing, Fig. 1 illustrates an embodiment of the invention in asimplified form for generating two harmonic frequencies. Fig. 2represents another embodiment of the invention in a more complex formfor generating any desired number of harmonic frequencies.

Referring to Fig. 1, a generator 10 is arranged to supply currents ofany desired fundemental frequency f to a pair of rectifying devices 11and 12. The devices 11 and 12 may be, for example, copper oxiderectifiers. The 30 generator 10 is coupled to the devices 11 and 12through a transformer 13 having primary and secondary windings, thesecondary wmding being divided into two portions. The

winding of the transformer 13 through a connection including a tunedcircuit 14 which is resonant to the frequency 7.

Another tuned circuit 15, resonant to the third harmonic frequency 3/,is bndged across the primary winding of the transformer 13. An outputcircuit for utilizing the third harmonic frequency may be conby means ofthe output terminals 18.

A tuned circuit 21, resonant to the second harmonic frequencv 27, isconnected between the dividing point in the secondary winding and apoint in the secondary circuit between the rectifying devices 11 and 12.A pair of is similar to that shown in output terminals 24 are providedfor use in connecting a load across the tuned circuit 21 for utilizingcurrent of the second harmonic frequency.

A biasing battery 27 is provided for suplying a suitable biasing currentto the rectiying devices 11 and 12. The biasing battery may be connectedin such a manner that the biasing currents are neutralized in thesecondary winding of the transformer 13 in order to avoid saturation ofthe magnetic circuit of the transformer.

The rectifying devices 11 and 12 are poled in such a manner that inrespect to the serially connected circuit including the secondarywinding of transformer 13 and the devices 11 and 12, the conductivedirections of the rectifying devices are opposed. In respect then to theparallel circuit including tuned circuit 21, battery 27 the two parts ofthe secondary winding of transformer 13 in parallel and the devices 11and 12 in parallel, the conductive directions of the devices 11 and 12are mutually aiding. 7

In the operation of the device of Fig. 1, the base frequency generator10 supplies a current of the frequency 7 through the tuned circuit 14and the transformer 13 to the rectifying devices 11 and 12. By virtue ofthe rectifying or modulating properties of the devices 11 and 12,electromotive forces of the various harmonic frequencies of thegenerator 10 are produced across the terminals of the devices.

The phase relationship of the harmonic voltages generated in therespective devices 11 and 12 is different for the harmonics of odd orderfrom what it is for the harmonics of even order.

The harmonic voltages of odd order are found to have phases related insuch a manner that they will aid in sending currents through thetransformer 13 from the second 'ary winding to the primary winding. Thebalanced arrangement of the secondary structure will prevent theelectromotive forces of odd order from producing current in the branchcontaining tuned circuit 21.

The electromotive forces of even order on the other hand are found tohave a phase relation such that they aid in sending currents through thecircuit branch containing tuned circuit 21. These currents are balancedin the secondary winding of the transformer 13 and are not transmittedto the primary winding.

Due to the phase relationships above described together with theselective nature of circuits 15 and 21 respectively, a current of thethird harmonic frequency is made available at the pair of terminals-18and a current of the second harmonic frequency is obtained at the pairof terminals 24.

Referring to Fig. 2, the

Fig. 1 except that system illustratedadditional provision is made forutilizing harmonic frequencies of the fourth, fifth and higher orders inaddition to those of the second and third orders. The circuitconstituents are for themost part the same as those shown in Fig. 1 andare designated by similar reference characters.

Tuned circuit 16, resonant to the fifth harmonic frequency 5f, isconnected in parallel with tuned circuit 15 and is provided with a pairof terminals 19 for connection to a load circuit.v Any desired number ofadditional branches may be added in a similar manner for utilizing thehigher harmonics. For example, a tuned circuit 17, resonant to thefrequency (2n 1) f, together with a pair of terminals 20 may he providedfor utilizing the (21?. 1)st harmonic.

Similarly, additional tuned circuits 22, 23

and others as desired may be provided in series with tuned circuit 21 toaccommodate the higher even harmonic frequencies and additional pairs ofterminals such as 25 and 26 may be added for connection to additionalload circuits.

What is claimed is:

1. In a system of harmonic generation, a source of electric current ofbase frequency, a transformer having a primary windingand a dividedsecondary winding, a secondary circuit including a pair of rectifyingelements serially connected with the secondary winding, the conductivedirections of the rectifying elements being mutually opposed, a supplycircuit tuned to the base frequency and adapted to connect the source tothe primary winding of the transformer, a' load circuit tuned to an oddharmonic of the base frequency and bridged across said primary winding,and a second load circuit tuned to an even harmonic of the basefrequency and connected between the dividing point of the said secondarywinding and a'point in the secondary circuit between said rectifyingelements.

2. In a system of harmonic generation, a source of electric current ofbase frequency. a transformer having a primary winding and a dividedsecondary winding, a secondary circuit including a pair of rectifyingelements serially connected with the secondary wind ing, the conductivedirections of the rectify and connected between the dividing point ofthe said secondary winding and a point the secondary circuit betweensaid rectifying elements.

3. Ina system of harmonic generation, a

source of electric current of base frequency, a transformer having aprimary winding and a divided secondary Winding, a secondary circuitincluding a pair of rectifying elements serially connected with thesecondary winding, the conductive directions of the rectifying elementsbeing mutually opposed, a supply circuit tuned to the base frequency andadapted to connect the source to the prlmary Winding of the transformer,21 group 01: load circuits respectively tuned to diflz'erent oddharmonics of the base frequency and bridged across said primary winding,and a second group of load circuits tuned respectively to difierent evenharmonics of the base frequency and connected in series between thedividing point of the said secondary winding and a point in thesecondary circuit between said rectifying elements.

In witness whereof, I hereunto subscribe my name this second day ofJune, 1930.

CLYDE R. KEITH.

